/usr/share/gocode/src/github.com/couchbase/moss/store_footer.go is in golang-github-couchbase-moss-dev 0.0~git20170914.0.07c86e8-4.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the
// License. You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an "AS
// IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
// express or implied. See the License for the specific language
// governing permissions and limitations under the License.
package moss
import (
"bytes"
"encoding/binary"
"encoding/json"
"fmt"
"time"
"github.com/edsrzf/mmap-go"
)
func (s *Store) persistFooter(file File, footer *Footer,
options StorePersistOptions) error {
startTime := time.Now()
if !options.NoSync {
err := file.Sync()
if err != nil {
return err
}
}
err := s.persistFooterUnsynced(file, footer)
if err != nil {
return err
}
if !options.NoSync {
err = file.Sync()
}
if err == nil {
s.histograms["PersistFooterUsecs"].Add(
uint64(time.Since(startTime).Nanoseconds()/1000), 1)
}
return err
}
func (s *Store) persistFooterUnsynced(file File, footer *Footer) error {
jBuf, err := json.Marshal(footer)
if err != nil {
return err
}
finfo, err := file.Stat()
if err != nil {
return err
}
footerPos := pageAlignCeil(finfo.Size())
footerLen := footerBegLen + len(jBuf) + footerEndLen
footerBuf := bytes.NewBuffer(make([]byte, 0, footerLen))
footerBuf.Write(StoreMagicBeg)
footerBuf.Write(StoreMagicBeg)
binary.Write(footerBuf, StoreEndian, uint32(StoreVersion))
binary.Write(footerBuf, StoreEndian, uint32(footerLen))
footerBuf.Write(jBuf)
binary.Write(footerBuf, StoreEndian, footerPos)
binary.Write(footerBuf, StoreEndian, uint32(footerLen))
footerBuf.Write(StoreMagicEnd)
footerBuf.Write(StoreMagicEnd)
footerWritten, err := file.WriteAt(footerBuf.Bytes(), footerPos)
if err != nil {
return err
}
if footerWritten != len(footerBuf.Bytes()) {
return fmt.Errorf("store: persistFooter error writing all footerBuf")
}
if AllocationGranularity != StorePageSize {
// Some platforms (windows) only support mmap()'ing at an
// allocation granularity that's != to a page size.
//
// However if on such platforms there are empty segments, then
// due to the extra space imposed by the above granularity
// requirement, mmap() can fail complaining about insufficient
// file space.
//
// To avoid this error, simply pad up the file up to a page
// boundary. This pad of zeroes will not interfere with file
// recovery.
padding := make([]byte, int(pageAlignCeil(int64(footerWritten)))-footerWritten)
_, err = file.WriteAt(padding, footerPos+int64(footerWritten))
if err != nil {
return err
}
}
footer.fileName = finfo.Name()
footer.filePos = footerPos
return nil
}
// --------------------------------------------------------
// ReadFooter reads the last valid Footer from a file.
func ReadFooter(options *StoreOptions, file File) (*Footer, error) {
finfo, err := file.Stat()
if err != nil {
return nil, err
}
fref := &FileRef{file: file, refs: 1}
// To avoid an EOF while reading, start scanning the footer from
// the last byte. This is under the assumption that the footer is
// at least 2 bytes long.
f, err := ScanFooter(options, fref, finfo.Name(), finfo.Size()-1)
if err != nil {
return nil, err
}
fref.DecRef() // ScanFooter added its own ref-counts on success.
return f, err
}
// --------------------------------------------------------
// ScanFooter scans a file backwards from the given pos for a valid
// Footer, adding ref-counts to fref on success.
func ScanFooter(options *StoreOptions, fref *FileRef, fileName string,
pos int64) (*Footer, error) {
footerBeg := make([]byte, footerBegLen)
// Align pos to the start of a page (floor).
pos = pageAlignFloor(pos)
for {
for { // Scan for StoreMagicBeg, which may be a potential footer.
if pos <= 0 {
return nil, ErrNoValidFooter
}
n, err := fref.file.ReadAt(footerBeg, pos)
if err != nil {
return nil, err
}
if n == footerBegLen &&
bytes.Equal(StoreMagicBeg, footerBeg[:lenMagicBeg]) &&
bytes.Equal(StoreMagicBeg, footerBeg[lenMagicBeg:2*lenMagicBeg]) {
break
}
// Move pos back by page size.
pos -= int64(StorePageSize)
}
// Read and check the potential footer.
footerBegBuf := bytes.NewBuffer(footerBeg[2*lenMagicBeg:])
var version uint32
if err := binary.Read(footerBegBuf, StoreEndian, &version); err != nil {
return nil, err
}
if version != StoreVersion {
return nil, fmt.Errorf("store: version mismatch, "+
"current: %v != found: %v", StoreVersion, version)
}
var length uint32
if err := binary.Read(footerBegBuf, StoreEndian, &length); err != nil {
return nil, err
}
data := make([]byte, int64(length)-int64(footerBegLen))
n, err := fref.file.ReadAt(data, pos+int64(footerBegLen))
if err != nil {
return nil, err
}
if n == len(data) &&
bytes.Equal(StoreMagicEnd, data[n-lenMagicEnd*2:n-lenMagicEnd]) &&
bytes.Equal(StoreMagicEnd, data[n-lenMagicEnd:]) {
content := int(length) - footerBegLen - footerEndLen
b := bytes.NewBuffer(data[content:])
var offset int64
if err = binary.Read(b, StoreEndian, &offset); err != nil {
return nil, err
}
if offset != pos {
return nil, fmt.Errorf("store: offset mismatch, "+
"wanted: %v != found: %v", offset, pos)
}
var length1 uint32
if err = binary.Read(b, StoreEndian, &length1); err != nil {
return nil, err
}
if length1 != length {
return nil, fmt.Errorf("store: length mismatch, "+
"wanted: %v != found: %v", length1, length)
}
f := &Footer{refs: 1, fileName: fileName, filePos: offset}
err = json.Unmarshal(data[:content], f)
if err != nil {
return nil, err
}
// json.Unmarshal would have just loaded the map.
// We now need to load each segment into the map.
// Also recursively load child footer segment stacks.
err = f.loadSegments(options, fref)
if err != nil {
return nil, err
}
return f, nil
}
// Else, invalid footer - StoreMagicEnd missing and/or file
// pos out of bounds.
// Footer was invalid, so keep scanning.
pos -= int64(StorePageSize)
}
}
// --------------------------------------------------------
// loadSegments() loads the segments of a footer. Adds new ref-counts
// to the fref on success. The footer will be in an already closed
// state on error.
func (f *Footer) loadSegments(options *StoreOptions, fref *FileRef) (err error) {
// Track mrefs that we need to DecRef() if there's an error.
mrefs := make([]*mmapRef, 0, len(f.SegmentLocs))
mrefs, err = f.doLoadSegments(options, fref, mrefs)
if err != nil {
for _, mref := range mrefs {
mref.DecRef()
}
return err
}
return nil
}
func (f *Footer) doLoadSegments(options *StoreOptions, fref *FileRef,
mrefs []*mmapRef) (mrefsSoFar []*mmapRef, err error) {
// Recursively load the childFooters first.
for _, childFooter := range f.ChildFooters {
mrefs, err = childFooter.doLoadSegments(options, fref, mrefs)
if err != nil {
return mrefs, err
}
}
if f.ss != nil && f.ss.a != nil {
return mrefs, nil
}
osFile := ToOsFile(fref.file)
if osFile == nil {
return mrefs, fmt.Errorf("store: doLoadSegments convert to os.File error")
}
a := make([]Segment, len(f.SegmentLocs))
for i := range f.SegmentLocs {
sloc := &f.SegmentLocs[i]
mref := sloc.mref
if mref != nil {
if mref.fref != fref {
return mrefs, fmt.Errorf("store: doLoadSegments fref mismatch")
}
mref.AddRef()
mrefs = append(mrefs, mref)
} else {
// We persist kvs before buf, so KvsOffset < BufOffset.
begOffset := int64(sloc.KvsOffset)
endOffset := int64(sloc.BufOffset + sloc.BufBytes)
nbytes := int(endOffset - begOffset)
// Some platforms (windows) only support mmap()'ing at an
// allocation granularity that's != to a page size, so
// calculate the actual offset/nbytes to use.
begOffsetActual := pageOffset(begOffset, int64(AllocationGranularity))
begOffsetDelta := int(begOffset - begOffsetActual)
nbytesActual := nbytes + begOffsetDelta
mm, err := mmap.MapRegion(osFile, nbytesActual, mmap.RDONLY, 0, begOffsetActual)
if err != nil {
return mrefs,
fmt.Errorf("store: doLoadSegments mmap.Map(), "+
"begOffsetActual = %v,"+
"nbytesActual = %v, sloc = %v, err: %v",
begOffsetActual, nbytesActual, sloc, err)
}
fref.AddRef() // New mref owns 1 fref ref-count.
buf := mm[begOffsetDelta : begOffsetDelta+nbytes]
sloc.mref = &mmapRef{fref: fref, mm: mm, buf: buf, refs: 1}
mref = sloc.mref
mrefs = append(mrefs, mref)
segmentLoader, exists := SegmentLoaders[sloc.Kind]
if !exists || segmentLoader == nil {
return mrefs, fmt.Errorf("store: unknown SegmentLoc kind, sloc: %+v", sloc)
}
seg, err := segmentLoader(sloc)
if err != nil {
return mrefs, fmt.Errorf("store: segmentLoader failed, footer: %+v,"+
" f.SegmentLocs: %+v, i: %d, options: %v err: %+v",
f, f.SegmentLocs, i, options, err)
}
if options.SegmentKeysIndexMaxBytes > 0 {
if a, ok := seg.(*segment); ok {
a.buildIndex(options.SegmentKeysIndexMaxBytes,
options.SegmentKeysIndexMinKeyBytes)
}
}
mref.SetExt(seg)
}
a[i] = mref.GetExt().(Segment)
}
f.ss = &segmentStack{
options: &options.CollectionOptions,
a: a,
refs: 1,
}
return mrefs, nil
}
// --------------------------------------------------------
// ChildCollectionNames returns an array of child collection name strings.
func (f *Footer) ChildCollectionNames() ([]string, error) {
var childNames = make([]string, len(f.ChildFooters))
idx := 0
for name := range f.ChildFooters {
childNames[idx] = name
idx++
}
return childNames, nil
}
// ChildCollectionSnapshot returns a Snapshot on a given child
// collection by its name.
func (f *Footer) ChildCollectionSnapshot(childCollectionName string) (
Snapshot, error) {
childFooter, exists := f.ChildFooters[childCollectionName]
if !exists {
return nil, nil
}
childFooter.AddRef()
return childFooter, nil
}
// Close decrements the ref count on this footer
func (f *Footer) Close() error {
f.DecRef()
return nil
}
// AddRef increases the ref count on this footer
func (f *Footer) AddRef() {
f.m.Lock()
f.refs++
f.m.Unlock()
}
// DecRef decreases the ref count on this footer
func (f *Footer) DecRef() {
f.m.Lock()
f.refs--
if f.refs <= 0 {
f.SegmentLocs.DecRef()
f.SegmentLocs = nil
f.ss = nil
}
f.m.Unlock()
}
// Length returns the length of this footer
func (f *Footer) Length() uint64 {
jBuf, err := json.Marshal(f)
if err != nil {
return 0
}
footerLen := footerBegLen + len(jBuf) + footerEndLen
return uint64(footerLen)
}
// --------------------------------------------------------
// segmentLocs returns the current SegmentLocs and segmentStack for
// a footer, while also incrementing the ref-count on the footer. The
// caller must DecRef() the footer when done.
func (f *Footer) segmentLocs() (SegmentLocs, *segmentStack) {
f.m.Lock()
f.refs++
slocs, ss := f.SegmentLocs, f.ss
f.m.Unlock()
return slocs, ss
}
// --------------------------------------------------------
// Get retrieves a val from the footer, and will return nil val
// if the entry does not exist in the footer.
func (f *Footer) Get(key []byte, readOptions ReadOptions) ([]byte, error) {
_, ss := f.segmentLocs()
if ss == nil {
f.DecRef()
return nil, nil
}
rv, err := ss.Get(key, readOptions)
if err == nil && rv != nil && !readOptions.NoCopyValue {
rv = append(make([]byte, 0, len(rv)), rv...) // Copy.
}
f.DecRef()
return rv, err
}
// StartIterator returns a new Iterator instance on this footer.
//
// On success, the returned Iterator will be positioned so that
// Iterator.Current() will either provide the first entry in the
// range or ErrIteratorDone.
//
// A startKeyIncl of nil means the logical "bottom-most" possible key
// and an endKeyExcl of nil means the logical "top-most" possible key.
func (f *Footer) StartIterator(startKeyIncl, endKeyExcl []byte,
iteratorOptions IteratorOptions) (Iterator, error) {
_, ss := f.segmentLocs()
if ss == nil {
f.DecRef()
return nil, nil
}
iter, err := ss.StartIterator(startKeyIncl, endKeyExcl, iteratorOptions)
if err != nil || iter == nil {
f.DecRef()
return nil, err
}
initCloser, ok := iter.(InitCloser)
if !ok || initCloser == nil {
iter.Close()
f.DecRef()
return nil, ErrUnexpected
}
err = initCloser.InitCloser(f)
if err != nil {
iter.Close()
f.DecRef()
return nil, err
}
return iter, nil
}
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